Alpine melt outran the stakes measuring it: ETH Zurich's tubes came free of the ice

An ablation stake is a bet on the coming summer: drill an aluminium tube deep enough into the ice that it is still standing in September, then read off how much of it the melt has exposed. Bauder has been placing them for twenty years, and his own account of the method is that he drills them deep enough to survive, except under conditions like this summer's ^[1][3]. The tube he pulled out of the Rhone was 4 metres long and the glacier's surface dropped by more than 9 ^[2][4], so the bet lost by better than a factor of two ^[1].

Re-drilling in the field fixes the immediate problem. It does not fix the siting. On a steep icefall at almost 2600 metres, where summer melt rarely reached in previous decades, the team found a second stake going over and put a new one in ^[5][6]. The melt line this year is above 3100 metres and climbing, which converts at least 500 metres of former accumulation zone into ablation zone ^[6][2]. That upper ground is what the whole accounting rests on: snow compacting into ice at the top, flowing down to offset the loss below ^[19]. Stakes were not up there because nothing much was leaving.

The season also began about twelve weeks early. Glacier loss day, the date summer melt overtakes winter snowfall in the Swiss Alps, fell on 2 July against a late-September norm ^[7][3], after a winter with scarce snow and a May heatwave ^[8]. Some of the loss is being driven from underneath. Ilaria Santin of ETH Zurich attributes the hole torn in the glacier's lower flank to meltwater draining down vertical shafts and building a subglacial river that collapsed the ice above it, and says more water at the bed means more ice going quickly ^[16][17].

The 6 per cent is the number worth keeping ^[10]. Straight-line arithmetic on that rate, which is a bound and not a projection, empties the Alps of ice in about 17 years ^[5]. On the same crude basis, Switzerland held roughly 2500 glaciers half a century ago, has lost more than 1000 of them, and the 30 the Swiss media expect to go this summer are around 2 per cent of the survivors ^[13][4]. The Rhone itself has pulled almost 2 kilometres back up its valley since it appeared in Goldfinger, far enough that the hotel built to look at it stands abandoned ^[18]. Anything sized to the melt rates of the last twenty years, a 4-metre tube included, is now sized wrong.